1. Field of the Invention
This invention relates to a device for automatically following a moving object in carrying out focus detection and focus adjustment in a camera and particularly in a video camera.
2. Description of the Prior Art
There have been proposed many automatic focus detecting devices of the kind arranged to use the video signal of a video camera as disclosed, for example, in the specifications of U.S. Pat. No. 2,831,057, Japanese Patent Publications No. SHO 39-5265 and No. SHO 46-17172, etc. These prior art devices employ different methods, which include one method called "a mountain climbing control method". This method was disclosed in an article entitled "Automatic Focus Adjustment of TV Camera by Mountain Climbing Servo Method", by Ishida, et al., appeared in "NHK Technical Researches", Vol. 17, No. 1 (Serial No. 86), p. 21, published 1965. Another method wherein mountain climbing control is employed in combination with a lens which is arranged to be focused by driving the rear lens thereof was disclosed in a technical report entitled "Contour Detecting Automatic Focusing Method", by Hanma, et al. at a conference of a TV Society held Nov. 29, 1983.
Referring to FIG. 1A of the accompanying drawings, the prior art devices of this kind have a distance measuring field fixedly positioned in the middle of a picture taking plane. Therefore, when a main object to be focused on, which in this instance is a person, (hereinafter referred to as the main object) moves, the camera is focused on a wrong object (a house in this instance) instead of the main object as shown in FIG. 1B. Then, the image of the main object becomes a blur. FIGS. 1A, 1B, 2A and 2B represent picture planes obtained with distance measurement performed by a camera which is provided with an automatic focusing device having no parallax.